/*
 * Copyright 2021 4Paradigm
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com._4paradigm.openmldb.importer;

public class MurmurHash {

    // all methods static; private constructor.
    private MurmurHash() {}

    /**
     * Generates 32 bit hash from byte array of the given length and
     * seed.
     *
     * @param data byte array to hash
     * @param length length of the array to hash
     * @param seed initial seed value
     * @return 32 bit hash of the given array
     */
    public static int hash32(final byte[] data, int length, int seed) {
        // 'm' and 'r' are mixing constants generated offline.
        // They're not really 'magic', they just happen to work well.
        final int m = 0x5bd1e995;
        final int r = 24;

        // Initialize the hash to a random value
        int h = seed^length;
        int length4 = length/4;

        for (int i=0; i<length4; i++) {
            final int i4 = i*4;
            int k = (data[i4+0]&0xff) +((data[i4+1]&0xff)<<8)
                    +((data[i4+2]&0xff)<<16) +((data[i4+3]&0xff)<<24);
            k *= m;
            k ^= k >>> r;
            k *= m;
            h *= m;
            h ^= k;
        }

        // Handle the last few bytes of the input array
        switch (length%4) {
            case 3: h ^= (data[(length&~3) +2]&0xff) << 16;
            case 2: h ^= (data[(length&~3) +1]&0xff) << 8;
            case 1: h ^= (data[length&~3]&0xff);
                h *= m;
        }

        h ^= h >>> 13;
        h *= m;
        h ^= h >>> 15;

        return h;
    }

    /**
     * Generates 32 bit hash from byte array with default seed value.
     *
     * @param data byte array to hash
     * @param length length of the array to hash
     * @return 32 bit hash of the given array
     */
    public static int hash32(final byte[] data, int length) {
        return hash32(data, length, 0x9747b28c);
    }

    /**
     * Generates 32 bit hash from a string.
     *
     * @param text string to hash
     * @return 32 bit hash of the given string
     */
    public static int hash32(final String text) {
        final byte[] bytes = text.getBytes();
        return hash32(bytes, bytes.length);
    }

    /**
     * Generates 32 bit hash from a substring.
     *
     * @param text string to hash
     * @param from starting index
     * @param length length of the substring to hash
     * @return 32 bit hash of the given string
     */
    public static int hash32(final String text, int from, int length) {
        return hash32(text.substring( from, from+length));
    }

    /**
     * Generates 64 bit hash from byte array of the given length and seed.
     *
     * @param data byte array to hash
     * @param length length of the array to hash
     * @param seed initial seed value
     * @return 64 bit hash of the given array
     */
    public static long hash64(final byte[] data, int length, int seed) {
        final long m = 0xc6a4a7935bd1e995L;
        final int r = 47;

        long h = (seed&0xffffffffl)^(length*m);

        int length8 = length/8;

        for (int i=0; i<length8; i++) {
            final int i8 = i*8;
            long k =  ((long)data[i8+0]&0xff)      +(((long)data[i8+1]&0xff)<<8)
                    +(((long)data[i8+2]&0xff)<<16) +(((long)data[i8+3]&0xff)<<24)
                    +(((long)data[i8+4]&0xff)<<32) +(((long)data[i8+5]&0xff)<<40)
                    +(((long)data[i8+6]&0xff)<<48) +(((long)data[i8+7]&0xff)<<56);

            k *= m;
            k ^= k >>> r;
            k *= m;

            h ^= k;
            h *= m;
        }

        switch (length%8) {
            case 7: h ^= (long)(data[(length&~7)+6]&0xff) << 48;
            case 6: h ^= (long)(data[(length&~7)+5]&0xff) << 40;
            case 5: h ^= (long)(data[(length&~7)+4]&0xff) << 32;
            case 4: h ^= (long)(data[(length&~7)+3]&0xff) << 24;
            case 3: h ^= (long)(data[(length&~7)+2]&0xff) << 16;
            case 2: h ^= (long)(data[(length&~7)+1]&0xff) << 8;
            case 1: h ^= data[length&~7]&0xff;
                h *= m;
        };

        h ^= h >>> r;
        h *= m;
        h ^= h >>> r;

        return h;
    }

    /**
     * Generates 64 bit hash from byte array with default seed value.
     *
     * @param data byte array to hash
     * @param length length of the array to hash
     * @return 64 bit hash of the given string
     */
    public static long hash64(final byte[] data, int length) {
        return hash64(data, length, 0xe17a1465);
    }

    /**
     * Generates 64 bit hash from a string.
     *
     * @param text string to hash
     * @return 64 bit hash of the given string
     */
    public static long hash64(final String text) {
        final byte[] bytes = text.getBytes();
        return hash64(bytes, bytes.length);
    }

    /**
     * Generates 64 bit hash from a substring.
     *
     * @param text string to hash
     * @param from starting index
     * @param length length of the substring to hash
     * @return 64 bit hash of the given array
     */
    public static long hash64(final String text, int from, int length) {
        return hash64(text.substring( from, from+length));
    }
}
